The present invention relates to stabilizer compositions for polyvinyl chloride resins and to polyvinyl chloride resin compositions having improved resistance to degradation caused by heat. Although capable of a variety of uses, this invention finds advantageous utility in providing improved long term stability at moderate temperatures to motor vehicle components shaped from polyvinyl chloride resin compositions, especially where the polyvinyl chloride resin compositions are used in combination with urethane.
The problem of imparting to polyvinyl chloride a sufficient heat processing stability at temperatures at which the polymer becomes sufficiently fluid or softened to permit shaping is of course of long standing, and has been satisfactorily resolved by addition to the polymer of various combinations of known heat stabilizers. At processing temperatures, the resin can degrade, liberating hydrogen chloride, and discolor, become brittle, and stick to the equipment. These problems are overcome by combining with the polymer before heat processing or during heat processing one or more of the well established and successful conventional heat stabilizers, such as, for example, organotin stabilizers and/or barium-cadmium or barium-zinc salt stabilizers.
Although the well established and successful conventional heat stabilizers provide effective stabilization to the polymer at elevated heat processing temperatures during standard processing, they may not provide effective stabilization to the polymer at lower more moderate temperatures after such heat processing. For example, protection against discoloration at moderate temperatures over long periods is a particular problem with motor vehicle components shaped from polyvinyl chloride resin compositions despite such compositions having contained conventional heat stabilizers during their heat processing. Depending upon their location in the vehicle, these components may be exposed to varied amounts of light, and also different rather high (above ambient) temperatures in use, and these differences can degrade motor vehicle components at differing rates. One result is the volatilization of one or more components, or of decomposition products therefrom, which condense as "fog" on interior surfaces such as the windows and windshield. Additionally, when polyvinyl chloride resin compositions are associated with a polyurethane foam backing, e.g. automobile instrument panels, glove compartments, door handles, arm and head rests, the amine from the urethane can contribute to discoloration of the polyvinyl chloride resin composition.